The Drum Rack previews aren't "patterns" at all and haven' been all the time I've been using Live (Version 7), they are prerecorded audiofiles (ogg). The Drum Racks category doesn't contain anmy MIDI.

You can browse the Clips category, those that are MIDI clips load the intended instrument or drum rack. But there's hundreds of clips, and no telling from the browser if what you're previewing is an audio or MIDI clip.

Or you can browse single Packs in the Places area: Expand a pack to look at the contents, some have a "Clips" or "MIDI Clips" folder inside.